Ion current measurements for Rb+, Rb+2 and Rb- ions allowed to characterize ionizing collisional processes involving excited atoms in a Rb vapour. Rate coefficients for these reactions are determined.
Negative ions are observed in a rubidium vapor when atoms are excited to the 6d level. Analysis shows that they correspond to the collision $\mathrm{Rb}(6d^{2}D_{\frac{5}{2}})+\mathrm{Rb}(5s)+\ensuremath{\Delta}E\ensuremath{\rightarrow}{\mathrm{Rb}}^{+}+{\mathrm{Rb}}^{\ensuremath{-}}$. The rate coefficient of the process is found to be (1.1\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}12}$ cm3 ${\mathrm{s}}^{\ensuremath{-}1}$ and the corresponding cross section 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ cm2.
Rb + and Rb 2 + formation in a laser-excited Rb vapour is extensively studied for s and d levels ranging from 5d to 11s levels. Collisional ionisation with a ground-state atom leads to Rb 2 + formation by Hornbeck-Molnar reaction with rate coefficients lying in the 10 -10 cm 3 s -1 range. This reaction is analysed theoretically. Penning ionisation occurs in collision with a resonant-state atom, Rb(5p), with a high efficiency (rate coefficient above 10 -8 cm 3 s -1 ). Associative ionisation between the 7s level and the 5p level is also observed (rate coefficient about 10 -10 cm 3 s -1 ). This reaction appears negligible for the neighbouring 5d level.
A frequency stabilized ring dye laser, with a linewidth of (TURN)250 kHz, has been utilized to selectively excite Rb(N('2)S, N('2)D) states in the range N = 20 - 100 by a two photon process. The highly excited atoms were detected by the technique of electric field ionization. Excited states with (VBAR)M(,L)(VBAR) < 3 have been observed to ionize along predominantly adiabatic paths and states with (VBAR)M(,L)(VBAR) (GREATERTHEQ) 3 have been observed to ionize along predominantly diabatic paths for the range of N investigated. The electric field dependence of the ionization threshold has been determined to be in good agreement with that calculated from a simple model based on the energies and ionization rates of hydrogen.\nCollisions between highly excited rubidium atoms and neutral xenon atoms, which result in a change in the N and L of the excited state of the rubidium atom, have been investigated. The N of the final state has been shown to be limited to those states which lie closest in energy to the initial state, in good agreement with theory. The distribution of L of the final states has been shown to be completely statistical or biased towards production of high L. The distribution of final L is definitely not biased toward production of states with low values of L.